A vehicle drivetrain transfers motive power from a power source to vehicle wheels. An engine is one example power source that includes a crankshaft. The crankshaft converts combustion energy from engine cylinders into rotational energy. In particular, combustion energy is transferred from the engine cylinders to pistons that linearly reciprocate. The pistons transfer the combustion energy to a crankshaft via rods, and the crankshaft converts the linear motion into rotational motion. The crankshaft may also include main bearing journals that are in mechanical communication with crankshaft bearings. The crankshaft bearings are captured between an engine block and the crankshaft. Lubrication flows from the engine block to the bearings, and the engine block supports the bearings and the crankshaft. The engine block and bearings allow the crankshaft and main bearing journals to rotate within the bearings. One example crankshaft is disclosed in U.S. Patent Publication No. 2005/0115524 which shows a four cylinder engine having five main bearings rotatably coupled to a crankshaft in the engine. The bearings guide crankshaft rotation and are mechanically coupled to an engine block that supports the crankshaft and bearings.
A crankshaft may flex and vibrate as torque is input to the crankshaft via connecting rods. Crankshaft flex may limit engine speed and increase engine vibration. One way to reduce crankshaft flexing and vibration is to provide a large number of main bearing journals along the length of a crankshaft so that the crankshaft can be supported at many locations. However, engine friction losses are proportional to a number of crankshaft bearing journals. Therefore, engine friction losses increase for each crankshaft bearing journal that is added to a crankshaft. As a result, the engine's power output and fuel economy may be substantially decreased as the number of bearing journals increase. Moreover, engine weight is increased for every additional crankshaft bearing journal. Consequently, engine block cost increases as a number of crankshaft main bearing journals increases.
To address at least some of the aforementioned issues a crankshaft is provided. The crankshaft includes an unsupported axially-aligned shaft section positioned between an outer main bearing journal and an inner main bearing journal, the unsupported axially-aligned shaft section having a central axis aligned with a rotational axis of the crankshaft, and a pendulum absorber coupled to the unsupported axially-aligned shaft section, the pendulum absorber including a blade extending from the unsupported axially-aligned shaft section and a pendulous counterweight coupled to the blade. The pendulum absorbers provide mass balancing to the crankshaft as well as increase the stiffness of the crankshaft in unsupported areas. As a result, noise, vibration, and harshness (NVH) may be reduced in the engine, thereby increasing customer satisfaction. Moreover, the longevity of the crankshaft may be increased when vibrations in the crankshaft are reduced. The pendulum absorbers also provide additional unloading of main bearing inertia forces.
In some examples, the pendulum absorbers are removably coupled to the unsupported axially-aligned shaft section via an attachment apparatus. Removably coupling the pendulum absorbers to shaft section increases the adaptability of the crankshaft, enabling the crankshaft to be used in a variety of engines.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings. It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.